Two-stroke internal-combustion engine



Nov. 4, 1924. 1,514,476

w. J. STILL v TWO-STROKE INTERNAL COMBUSTION ENGINE Filed Sept. 1, 1921 Patented Nov. 4, 19524. i v

' wI Lmm JOSEPH: STILL, or ronnon, nnerann.

mwo-s'rnoxin INTERNAL-COMBUSTION Enema Application filed September I '0 all whom it may concern:

Be it known that I, WILLIAM JOSEPH S'r1LL, a subject of the King of Great Britain, and resident of London, England,

have invented certain new. anduseful Improvements in and Relating to, Two-Stroke Internal-Combustion Engines, of which the following is a specification. l This invention relates to two stroke internal combustion engines of that character wherein inlet and exhaust ports are uncovered by the engine piston. In such engines as hitherto constructed the exhaust 1 port has necessarily been so desi nedand located relative to the inlet port t at it is uncovered by'the engine piston slightly before the inlet port is uncovered to admit -the scavenging air charge andof course closes after the inlet port has closed. It follows as a consequence that after the inlet port has closed there'is an escape of some portion of the charge within the cylinder the charge escaping until the exhaust port has also closed.

The effect of this is to reduce the weight of the charge within the cylinder. It has been suggested to counteract this by raising the pressure of the scavenge air and another method which has been suggested is-to provide a throttling valve in the exhaust pipe ofthe engine. The present invention also has for its object to provide a two stroke internal combustion engine in which the weight of the air charge retained within the cylinder is increased beyond that possible with the usual construction, and consists broadly of a two stroke internal combustion engine having an auxiliary exhaust or pressure releasb port adapted to be opened prior to the opening of the main exhaust port. A further feature of the invention consists in so arranging theo scavenging charge inlet port that it will be uncovered by the engine piston prior to the uncovering of the exhaust, and providing means for lowering the'pressure in the cylinder before the end of the expansion stroke.

The invention further'comp-rises a twostroke internal combustion engine in which the engine piston acts as a valve over the inlet and exhaust ports, wherein communication between the cylinder and the exhaust outletv is cut ofi' prior to cutting ofi communication between the cylinder and the scavenging .charge inlet, and established prior to establishing communication between 1, 1921. fierial No. 497,700.

the cylinder and the scavenging charge inst. v

In the embodiment-of the invention illustrated by the accompanying drawing the charge inlet or scavenging port 1 of the cylinder 3 is so disposed relatively to the-exhaust port 2 that the inlet port 1, during the outward stroke of the piston 4, will be uncovered prior'to the uncovering of the exhaust port 2, and will be closed by the piston 4 during its return stroke, after the closing of the exhaust port 2.

The cylinder 3 is provided with a release port '5 having a cylindrical portion 6 bored. to receive a piston valve 7. This valve is operated from the cam shaft ofthe engine by a connecting rod 8 connected to a can or other suitable device on the cam shaft or driven therefrom in anysuitable manner.

During the. expansion stroke of the en--- gine, the release valve 7 opens and the gases within the cylinder escape by their own pressure when the piston uncovers the release ports in the cylinder wall, and the pressure within the cylinder '3 falls to or below atmospheric pressure. The inlet scav'-. enge port 1 is then uncovered followedimmediately after by the uncovering of the. exhaust ort 2 and scavenging isefifected' in the usual way. The release valve 7 is closed and the exhaust port 2 is'again covered prior to final closure of the inlet port 1 and thus there is a rise of pressure in 'the scavenge lows that the charge within the c linder 3 of the piston from the point of closure of the exhaust port 2 at a pressure something above atmospheric pressure. Thus -the weight of charge will be increased for two reasons. In the first. place it will be increased by thegreater swept volume consequent upon the exhaust port 2 being lower than the inlet port 1 and secondly it will, be at an increased pressure without involving any increase in the scavenge pump pressure. The clearance space between the piston valve 4 and the engine cylinder 3 can be very small and moreover the work done in compression into this space will not be wasted since any compressed air in this space will be -re-expanded; 'with the movenient of the piston valve,

What- I claim and desire tens-Patent is A two stroke internal combustion engine to secure by Let- 'will be the full swept volume of t e'stroke comprising a cylinder, a series of openings in the wall of said cylinder adapted to constitute a scavenging charge inlet port, a fur ther seriesof openings in the wall of the cylinder on the opposite sideof said inlet port adapted to constitute a main exhaust port. a piston reciprocable in said cylinder and adapted to' function as a valve for opening and closingsaid inlet and exhaust ports, the openings constituting the inlet port being of greater depth than the opening constituting the main exhaust port whereby said inlet openings are uncovered by the piston on its expansion stroke earlier than the main exhaust port openings and covered by such -piston on its compression stroke later than .open on the expansion stroke of the piston so as to lower the pressure in the cylinder before the main exhaust port is uncovered and to close upon the compression stroke of the piston whereby the inlet port remains open for a short period after both exhaust ports are closed.

In witness whereof I afiix my signature.

WILLIAM JOSEPH STILL. 

